Satellite DNA's and other simple, tandemly-repeated nucleotide sequences, are present in or about the centromeric heterochromatic region of the chromosomes of man, and numerous other eukaryotes. Their functions are unknown. We seek support to continue our studies of satellite DNA's in Drosophila. We will employ established biochemical, genetic, and cytological procedures to extend our investigation of satellite DNA's. The proposed experiments may provide information about: 1) the nucleotide sequence of two newly-discovered satellites, and their possible relationship to the nucleotide sequence of the major satellites of D. virilis; 2) DNA sequences at the boundary between satellite-containing heterochromatin and main band containing euchromatin; 3) the arrangement of satellite DNA sequences along the chromosome; 4) satellite DNA-binding chromosomal proteins; 5) satellite DNA-associated chromosomal proteins. Since satellite DNA's are a chromosomal feature common to Drosophila and to man, there is an excellent possibility that these experiments will provide information applicable to the problem of the organization and molecular architecture of human chromosomes.